4.
[tex]a)sa \: se \: arate \:ca \frac{1}{ \sqrt{2} + \sqrt{3} } = - \sqrt{2} + \sqrt{3} \\ b)b.sa \: se \: calculeze \: numarul \: \: s = \frac{1}{1 + \sqrt{2} } + \frac{1}{ \sqrt{2 + \sqrt{3} } } + ... + \frac{1}{ \sqrt{2017 + \sqrt{2018.} } } [/tex]
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